The present invention relates to assemblies of cords used to reinforce plastic and/or rubber materials and to articles, such as reinforcement plies, belts, tubes and pneumatic tires which embody such reinforcement assemblies.
It is well known that when these assemblies have a complex structure formed at least in part by a core and two layers surrounding said core, it is difficult to achieve a uniform, compact structure for the following reasons: either the imbricating of the cords of one layer in another layer is excessive or the space available for the cords of the outer layer is insufficient. In both cases this results in a disorganization of the assembly since certain cords have an unstable condition. Upon the production of articles by the combining of these assemblies with plastic and/or rubber materials, in particular by a calendaring operation, the pressure exerted on the assembly causes a displacement of these unstable cords the length of which becomes excessive, resulting in the formation of intermittent loops and poor dynamic behavior of the articles. Moreover, this disorganization adversely affects the mechanical properties of the assembly as the result of a non-uniform distribution of the stresses.
The object of the invention is to avoid these drawbacks. Toward this end, the reinforcement assembly according to the invention is characterized by the following features when it is so arranged that its axis is rectilinear:
(a) it has a core formed of a layer of cords or of a center surrounded by a layer of cords, said layer of cords being referred to as the "core layer" in both cases; PA1 (b) it has two adjacent layers of cords surrounding the core layer, the layer closest to the core being referred to as the "intermediate layer" and the layer furthermost from the core being called the "outer layer"; PA1 (c) the intermediate layer and the outer layer are each formed of cords wound around the axis of the assembly in the same direction and with the same pitch; PA1 (d) the intermediate layer and the outer layer have the same direction of winding and the same pitch; PA1 (e) the core layer is formed of cords which are: PA1 (f) the cords of each layer have the same diameter; PA1 (g) in the intermediate layer, the axis of each cord is disposed substantially around the axis of the assembly along a helix such that the ratio between the radius of curvature of said helix and the diameter of said cord is less than 75; PA1 (h) the intermediate layer includes a residual space, the ratio between the size of said residual space and the diameter of the cords of the outer layer being at least equal to 0.30 and at most equal to 0.45; PA1 (i) the number of cords of the outer layer is at least 15.
parallel to the axis of the assembly; or PA2 wound around the axis of the assembly in the same direction and with the same pitch, the directions of winding of the core layer and the intermediate layer being opposite; or PA2 wound around the axis of the assembly in the same direction and with the same pitch, this direction being the same as that of the intermediate layer, the core layer and the intermediate layer having pitches which differ in such a manner that the ratio between the difference in the values of these two pitches to the larger value of these two pitches is equal to at least to 0.30;
The following description with reference to the drawings illustrates the invention and facilitates an understanding of it, without limiting its scope.